In problem constrained scaling, the problem sized is kept fixed, regardless of the number of processors on the machine.

In time constrained scaling, the wall-clock execution time needed to complete the program is kept fixed. The problem is scaled so that the new problem's execution time on a large machine is the same as as the old problem's execution time on a small machine.

In memory constrained scaling, the amount of main memory user per processor is kept fixed. The problem is scaled so that the new problem uses exactly k time as much main memory as the old problem.

CaptainBlueBear

With problem-constrained scaling, speedup = time by 1 processor/time by P processors